1. Field of the Invention
The present invention relates to a sheet processing device, an image forming system, and a sheet processing method.
2. Description of the Related Art
Recent digitization of information requires image processing devices such as a printer and a facsimile used for outputting digitized information and a scanner used for digitizing documents. Such an image processing device is often configured as a multifunction peripheral that can be utilized as a printer, a facsimile, a scanner, and a copying machine, having an imaging function, an image forming function, and a communication function, for example.
Among such multifunction peripherals, known is a multifunction peripheral on which a folding processing device is mounted. The folding processing device forms an image on a fed sheet to draw the image and performs folding processing on the sheet on which the image is formed. When such a folding processing device performs folding processing on the sheet, a fold is weak and incomplete, and a folding height is high. Accordingly, among such multifunction peripherals, known is a multifunction peripheral on which a fold-enhancing device is mounted in addition to the folding processing device. The fold-enhancing device performs fold-enhancing processing for enhancing the fold by pressing the fold formed through the folding processing to enhance the fold and reduce the folding height (for example, refer to Japanese Laid-open Patent Publication No. 2007-045531 and Japanese Laid-open Patent Publication No. 2009-149435).
When the folding processing device as described above performs folding processing on the sheet, a fold is generally formed in a direction (hereinafter, also referred to as a “main scanning direction”) perpendicular to a conveying direction of the sheet (hereinafter, also referred to as a “sub-scanning direction”).
Examples of a method for performing fold-enhancing processing by the fold-enhancing device as described above include a method for pressing the fold formed on the sheet while conveying the sheet with a fold-enhancing roller having a length corresponding to a sheet width that is laterally bridged in a direction (main scanning direction) parallel to the fold formed through the folding processing.
Examples of another method for performing fold-enhancing processing by the above-described fold-enhancing device include a method for sequentially pressing a fold formed on a sheet in a main scanning direction by temporarily stopping conveyance of the sheet at a position where fold-enhancing processing is performed, and moving the fold-enhancing roller rotating about a direction (sub-scanning direction) perpendicular to the fold formed through the folding processing as a rotation axis, in the main scanning direction on the stopped sheet.
In the former method for performing fold-enhancing processing described above, a plurality of fold-enhancing rollers need to be arranged in the conveying direction of the sheet. This is because a pressing force is dispersed across the entire fold by pressing the entire fold with one fold-enhancing roller at one time and a pressing force per unit area becomes small, and a sufficient fold-enhancing effect cannot be obtained with one fold-enhancing roller. Accordingly, with the method of pressing the fold formed on the sheet while conveying the sheet with the fold-enhancing roller having a length corresponding to a sheet width that is laterally bridged in the main scanning direction, a space is required to arrange a plurality of fold-enhancing rollers. Thus, the size of a multifunction peripheral is increased and the number of driving systems and control systems for driving the fold-enhancing rollers is increased, which increases initial costs and running costs.
On the other hand, in the latter method for performing fold-enhancing processing described above, the entire fold is successively pressed in the main scanning direction with one fold-enhancing roller, so that a pressing force is not dispersed because the pressing force can be intensively applied to the entire fold. However, during the fold-enhancing processing, the fold-enhancing roller needs to be moved from one end to the other end of the sheet width direction while the sheet is stopped. Accordingly, with the method for successively pressing the fold formed on the sheet in the main scanning direction by moving the fold-enhancing roller rotatable about the sub-scanning direction as a rotation axis, in the main scanning direction on the stopped sheet, time is required for moving the fold-enhancing roller from one end to the other end of the sheet width direction, and thus productivity is reduced. The problem described above occurs not only with the sheet for image formation output, but also with a sheet-like object in some cases. The problem described above is caused not only in a case of enhancing the fold of the sheet in a folded state, but also in a case of pressing the sheet.
In view of the above, there is a need to provide a small, low-cost, highly productive sheet processing device for pressing a sheet.